In recent years, recording media are increasing in capacity. As the capacities of recording media increase, the reproduction environment becomes stricter. For example, an optical recording medium achieves a large capacity by improving the line density of record marks, forming an information recording layer having a multilayer structure, and the like. On the other hand, reproduced data readily includes errors, resulting in deterioration of the reproduction environment. Hence, there is demanded a signal processing technique capable of accurately reconstructing reproduced data even under such a reproduction environment.
There have been proposed various kinds of error correcting code methods to correct errors in data in recording/reproduction systems and communication systems. An LDPC (Low Density Parity Check) code is known to have an excellent error correcting capability. In particular, the LDPC code exhibits an outstanding characteristic for random errors. However, the LDPC code does not necessarily exhibit a satisfactory characteristic for burst errors (continuous errors) that occur due to defects in a recording medium or the like. For this reason, particularly when applying the LDPC code to a recording/reproduction system, improved resistance to burst errors has been demanded.